A British man has been detained in Ukraine on suspicion of spying for Russia, the Ukrainian security service has said.

Its investigation into the suspect, said to be a former member of the British armed forces, was carried out in coordination with British intelligence, a security source said.

The man, who has been named in local media reports, travelled to Ukraine early last year to work as an instructor training the Ukrainian military, according to a statement by Ukraine's SBU.

However, it alleged that he was then recruited by Russia's FSB spy agency, lured by the promise of making "easy money".

In an extraordinary list of allegations, the Ukrainian security service accused the man of passing official information about the Ukrainian military to the Russian spy agency.

Planned terrorist attacks

It also claimed that he was preparing to commit terrorist attacks.

Among the information he is alleged to have shared with the Russians are the coordinates of military training centres in the south of Ukraine and details about foreign instructors working for the Ukrainian armed forces.

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The man is also accused of receiving instructions on how to make an improvised explosive device, as well as being told where to find a pistol with two loaded magazines. He was detained in October.

The SBU first released details then, but further information on his case emerged today when Ukrainian media reported his name.

He is being held under suspicion of passing unauthorised information to Russia. If found guilty, he could face up to 12 years in prison.

Sky News has contacted the Foreign Office for comment.